Fuses are commonly used as circuit protection devices. A fuse can provide electrical connections between sources of electrical power and circuit components to be protected. One type of fuse includes a fusible element disposed within a hollow fuse body. Conductive terminals may be connected to different ends of the fusible element through the fuse body to provide a means of connecting the fuse between a source of power and a circuit component.
Upon the occurrence of a specified fault condition in a circuit, such as an overcurrent condition, the fusible element of a fuse may melt or otherwise separate to interrupt current flow in the circuit path. Portions of the circuit are thereby electrically isolated and damage to such portions may be prevented or at least mitigated.
As a fuse element melts, material of the element vaporizes and can deposit inside the fuse housing. This can lead to a low resistance current path between the fuse terminals. Said differently, even when the fuse element has melted and/or separated, the fuse terminals may still be electrically connected via a low resistance through the deposits of the vaporized fuse element on the inside of the fuse housing. These low resistance electrical paths are often referred to as “carbon bridges.” As will be appreciated, carbon bridges can allow leakage current to flow between the fuse terminals. As such, when a carbon bridge forms, the fuse does not provide enough insulation resistance to protect the circuit components. Furthermore, as circuit voltage increases, so does the chance or occurrence of carbon bridges. In particular, owing to the high energetic light arc occurring when high voltage fuse elements vaporize, the occurrence of carbon bridges also tends to increase.
As will be appreciated, carbon bridges, and particularly the resulting leakage current, can damage circuit components intended to be protected by the melting of the fuse element. Accordingly, having a high insulation resistance in a fuse after melting of the fuse element is useful. In particular, some standards exist specifying insulation resistance to be greater than a specific value (e.g., >1 MΩ after melting at 70V, or the like) in order for the fuse to be compliant with the standard.